Platelets are one of the corporeal components of the blood having important significance with respect to hemostasis and thrombus formation in the body. Platelets are released into the blood from mature megakaryocytes formed from hematopoietic stem cells in bone marrow via megakaryocytic precursor cells and megakaryoblasts.
Factors having two different types of action are considered to be required to form megakaryocyte colonies from myeloid cells (Williams, N. et al., "J. Cell Physiol.", 110, 101 (1982)). More specifically, these factors consist of Meg-CSF, which by itself result in the formation of megakaryocyte colonies, and Meg-POT, which, although does not result in the formation of megakaryocyte colonies by itself, increases the number of megakaryocyte colonies and promotes their maturation when added together with Meg-CSF.
In human, IL-3 (Teramura, M. et al., "Exp. Hematol.", 16, 84 (1988)) and granulocyte-macrophage colony stimulating factor (Teramura, M. et al., "Exp. Hematol.", 17, 1011 (1989)) have Meg-CSF activity. In addition, examples of substances having Meg-POT activity in human include interleukin 6 (Teramura M. and Mizoguchi, H. "Int. J. Cell Cloning", 8, 245 (1990)), interleukin 11 (Teramura, M. et al., "Blood", 79, 827 (1992)), and erythropoietin (Bruno, E. et al., "Blood", 78, 671 (1989)).
However, it is also known that these substances are not specific factors for the megakaryocyte-platelet lineage, but rather also act on other blood cells as well as on cells outside the blood cell system. Thus, in the case of administration of these substances as pharmaceuticals in anticipation of their action on the megakaryocyte and platelet systems, there is also the risk of the manifestation of other actions different from that which is expected. As such, there is a need for a physiologically active substance having a high degree of usefulness as a pharmaceutical product that specifically acts on the megakaryocyte-platelet system.